Piston for internal combustion engines



Sept. 2, 1941.

B. GRAHAM PISTON FOR INTERNAL COMBUSTION ENGINES 2 Sheets-Sheet 1 Filed Oct. 5, 1937 E. aham p 2, 1941- E. B. GRAHAM 2,255,006

PISTON FOR INTERNAL COMBUSTIQN ENGINES Filed Oct. 5, 1937 2'Sheets-Sheet 2 Patented Sept. 2, 1941 Eric Bradley Graham, Friern Park, North Finclh ley, London, England, assignor to Specialloid, Limited, London, England Application October 5, 1937, Serial No. 167,462 In Great Britain September 28, 1936 Claims.

This invention relates to light alloy pistons for internal combustion engines. I

It has been found in connection with such pistons that certain advantages, are secured by furnishing in the structure of the piston a ring of cast iron or steel of an austenitic character particularly in the case of pistons for compression ignition engines.

Certain prior proposals in connection with light alloy pistons have involved modification of the composition of the light metal alloy and the employment of cast iron of a composition such that the co-eflicient of thermal expansion of the the light alloy may have a co-eiiicient of thermal expansion of about 0.000022 while the-iron alloy has a co-efiicient of thermal expansion 01' Other proposals have involved, inter alia, the fitting of a light alloy piston with a piston ring carrier in the form of a steel ring of undefined thermal properties upon the head of a pistonin 'to extend above the topmost compression ring groove that it is necessary to provide against any slackness arising in operation by forming the carrier ring with castellations, a similar construction being also desirable where austenitic iron having a co-e'mcient of expansion similar to that of the material forming the body of the piston is used.

The invention is based upon the observation that an unbroken ring of cast iron or steel of an austenitic character extending above the top of the compression ring and incorporated in the structure of the piston, in consequence of the relatively low rate of heat conductivity of austenitic iron and steel, and of the fact that it becomes surrounded by a film or skin of oxide in the casting of the body of the piston, operates to baille the direct heat flow from the head of the piston to the topmost and the next succeeding row ofgrooves in which compression rings are arranged.

A further observation on which the invention or compression rings.

such manner as to secure a positive lock with the a groove or grooves for the accommodation of the compression ring, it has been suggested to use a material such as a nickel-iron alloy having a low co-eiiicient of expansion to heat, that is to say, having a much smaller thermal coeificient of expansion than the iron of which the 0 cylinder is formed, and further, has a lower coeflicient of expansion to heat than the material forming the piston body, there being left between the ring and the adjacent portion of the body of the piston suilicient play so that the ring shall not be affected by the thermal expansion of the piston.

In another instance it has been suggested to employ gray cast iron or austenitic iron of particular compositions and it has been noted that where gray cast iron is employed to form 'a carrier for the compression rings and is arranged 5 A further observation on' which the invention is based is that austenitic iron or steel possessing a thermal co-eiilcient of expansion very considerably less than that of the light alloy may be employed in the formation of light alloy pistons having an aluminium or magnesium base in forming an insert 'or ring adjacent to the head of the piston and that, for instance, the difl'erence of the co-efilcientof expansion between the light metal alloy and the austenitic iron or steel may amount to 20% of the former.-

The invention consists, broadly, in light alloy pistons for internal combustion engines and particularly for compression ignitioneenginesin the structure of which is furnished an unbroken ring of cast iron or steel of an austenitic character at a position to function as a heat baflle between the head of the piston and the uppermost compression ring and having a co-efiicient of expansion to heat which is more than 10% less than that of the light metal alloy and may be in the neighbourhood of 20% less than that of the light alloy.

Generally, the cast iron or steel of an austenitic character employed in accordance with the invention, has a thermal co-eflicient of expansion of 0.000016 to 0.000019 per C. and generally that the insert is kept securely in position tends, and in this case the insert may not greater than 0.000018, while the light metal rials have a similar co-efllcient of expansion the grip on the width of the insert is very small, whereas a very definite contraction grip is obtained by the employment of austenitic iron' or steel, in accordance with the invention, having a co-efficient of expansion to heat differing widely from that of the light metal alloy although the grip is within the elastic limit of the latter.

Thus, a very definite advantage is secured in with the result that the risk of the insert becoming slack owing to-inertia and general wear is minimised.

As an example of the composition of an austeniti'c cast iron which may be used in accordance with the invention, the following particulars are given:

Where, in accordance with the invention, the insert is in the form of an annulus which is provided with grooves for the accommodation -of compression ring or rings, the annulus is preferably furnished onits inner face and adjacent to its upper extremity with a flange provided with one or more recesses leaving between the recesses radially extending projections.

For instance, such a ring may be of 185.25 mm. external diameter with a maximum internal diameter of 156.5 mm. and a diameter within the extremities of the flange of 148.5 mm. and in the flange are produced by means of a rotary cutter or circular form and 2" in diameter, recesses spaced apart from one another at an angle of 45, the maximum depth of each of such recesses being equivalent to the width of the flange. As above indicated, in accordance with the invention, the insert may be in the form of a ring or annulus which is not provided with recesses for the accommodation of compression rings.

In this case the ring or annulus is located in the piston above the level at which the compression rings are provided and it may extend into the-piston head through a relatively considerable 'depth, that is to say, for a distance greater than that which an insert of the more usual form exalso be relatively thin.

Conveniently, it is of dished or somewhat conical form with the portion directed to the apex extending away from the piston head.

With such a construction, while preferably ausefficient of expansion to heat corresponds more or less closely with that of the austenitic cast iron or steel employed.

The invention will be described further in detail and by way of example with reference to the accompanying drawings in which- Figure 1 is a view in sectionalelevation of one construction of piston in accordance with the invention,

Figure 2 is a view in sectional elevation of the insert therein, t Figure ,3 being a view'in sectional elevation on the line III-Ill of Figure 2,

Figure 4 being a plan view of the insert, while Figure 5 is a view in sectional elevation of an alternative construction of piston in accordance:

with the invention.

Referring to Figures 1 and 5 of the drawings, in the body of the piston I which is formed in a light metal alloy and, for instance, an alloy having a content of 4 per cent. of'copper, 2 per cent. of nickel, 1 per cent. of magnesium, the

balance being aluminium, the co-eflicient of expansion to heat of which at 20 C. will be 0.000022 per 0., adjacent to the head there is engaged a ring or annulus 2 formed of an austenitic cast iron of thecomposition and having a co-eflicient of expansion of the character above indicated. In the case of the construction shown in Fig- .ures 1, 2, 3 and 4, the annulus is provided with grooves 3 for the accommodation of compression rings on its outer face, and on its inner face it is furnished, adjacent to its upper extremity, with a flange 4, provided with a plurality of recesses 5 which leave between the recesses more or less radially extending projections, the recessesin the flangq being produced by means of a rotary cutter of circular form.

In the case of a ring having an external diameter of 185.25 mm. the other dimensions thereof and the dimensions of the rotary cutter used in producing the recesses in the flange and its mode of use may be as indicated on the more general description given above.

In the case of the construction illustrated in Figure 5, the ring or annulus 2 is located above the level at which the topmost groove 5 for the tenitic cast iron or steel having a relatively low M co-eflicient of expansion is employed,- the invention extends to the use of austenitic cast iron or steel such as has previously been proposed to be used in forming light iron or steel inserts, or thecomposition of the light metal alloy may be varied so that its cometal alloy pistons with accommodation of a compression ring is located and it extends into the body of the piston head through a relatively considerabledistance, that is to say, for a distance greater than that which an insert of the more usual form would extend, the insert in the case of the construction illustrated being relatively thin and of dished or somewhat conical formation with the portion directed to the apex extending away from the piston head.

I claim:

1. A piston for an internal-combustion engine comprising a cylindrical body portion formed of a light metal alloy and a ring of an ironalloy of an austenitic character engaged in the body portion at a position to function as a heat baflie between the head of the piston and the uppermost compression ring said iron alloy having a coeflicient of expansion to heat which is between the limits of 10 per cent and 20 per cent less than that of the light metal alloy.

2. A piston for an internal combustion engine comprising a cylindrical body portion formed of a light rmetal alloy having a coefllcient of exv iron alloy having a coefiicient of expansionto formed of a light metal alloy, and an externally grooved ring formed of an iron alloy of an austenitic character engaged in the said body portion adjacent to the head thereof, said iron alloy having a co-efficient of expansion-to heat which is between the limits of 10 per cent and 20 per cent less than the coefficient of expansion to heat of the light metal alloy. I

5. A piston for an internal combustion engine, comprising a cylindrical body portion formed of a light metal alloy, a ring of an iron alloy of austenitic character embedded in said portion adjacent to the head thereof and extending above the level at which the uppermost compression ring will be located, said iron alloy having a coefiicient of expansion to heat which is between the limits of 10 per cent and 20 per cent less than the coefl'icient of expansion to heat of the light metal alloy.

ERIC BRADLEY GRAHAM. 

